I would like to add Na+ inactivation to the sodium calcium exchanger mod file - https://senselab.med.yale.edu/ModelDB/M ... l?id=88209 - which is based on Courtemanche et al Am J Physiol 1998 275:H301. NCX can inactivate during high intracellular Na+ levels and I would like to experiment with how this alters input-output transformation in various cells. However, I'm unsure how to tackle this (I'm very new to Neuron but experienced Python programmer). It appears that adding a state variable to the model that represents the inactivation state by nai (both cai and nai are already READ in the model) would be required and then solving the rate of inactivation in a Breakpoint statement based on the time dependence of inactivation would be the way to go, but I wanted to know if I was on the right track? and secondly, I wanted to inquire (mainly out of curiosity) if this could also be tackled using Python from within the main init.py file? thanks in advance for any help

The link you provide is not to the file that implements the Na-Ca exchange mechanism--instead, it produces a list of ModelDB models "that contain the Current : Na/Ca exchanger". None of them happens to be by Courtemanche et al., which is very strange indeed, since the very paper by Courtemanche et al. that you mention has an entry in ModelDB! We're going to have to fix that . . .

Anyway, going straight to the Courtemanche et al. model entry (model 3800 in ModelDB), I see a file called nacaex.mod, and the first line in that file is
TITLE sodium calcium exchange
so presumably this is the NMODL source code for the Na-Ca exchanger that you are interested in.

I'm unsure how to tackle this (I'm very new to Neuron

Best for it to be done in NMODL, which isn't Python. Provide a mathematical description of inactivation and I'll do it for you. Either point me to a paper that presents such a description, or post it in your reply to this message on the Forum, or email it to me.